The Sanjiang Plain is the largest and most concentrated wetland region in China, the total area is about1. 088×107ha with rich marsh resources and biodiversity. Before 1949, the Sanjiang Plain was a large untravelled wild plant and waterfowl habitat, and there were some rare swans, red-crowned cranes and thousands of hydrophytes. From 1950, the local government began to reclaim the marsh in the Sanjiang Plain, built the commodity grain base of Northeast China, and developed the industry of grain processing, animal husbandry, etc. Up to now, there are 54 farms which control 3. 5087×106ha agriculture field. The marsh areas are reduced by 1/2; many rare animals and plants are near extinction. The human activities and agriculture reclamation made a great change on the environment, especially made water balance change and regional climate change. So to study and protect the wetland ecosystem and marsh resource are extremely urgent. This paper focus on the hydrology change and climate change before and after marsh reclamation, including evapotranspiration, run off, soil character, micro-climate on both marsh and agriculture field, and the reason that cause seasonal drought, waterlogging and degeneration of marsh.